Method and apparatus for heat interchange with compressed gases



y 1936; H. HOLZWARTH 2,040,090

METHOD AND APPARATUS FOR HEAT INTERCHANGE WITH COMPRESSED GASES Filed July 18, 1935 4 Sheets-Sheet 1 lnuenfar 'ay 12, 1936. H. HOLZWARTH 2,040,090

METHOD AND APPARATUS FOR HEAT INTERCHANGE WITH COMPRESSED GASES Filed July 18, 1933 4 Sheets-Sheet 2 v I 6 I A W 'd -fl fl 4 4 0 8 m A? Invemor H. HOLZWARTH METHOD AND APPARATUS FOR HEAT INTERCHANGE WI H COMPRESSED'GA'SES Filed July 18, 1933 4 Sheets-Sheet 5 w a W k 7 v i 7.010 z 8 w i ii 3 z 7 "W T 7 7. W W 3 .5 7. Z 7. \v '//P /r/// r //4 m z 7.

May 12, 1930' HQHOLZAWARTH METHOD AND APPARATUS FOR HEAT INTERCHANGE WITH COMPRESSED GASES Filed July 18, 1953 4 Sheets-Sheet 4 .wvvi

lll'lll Patented May 12, 1936 UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR HEAT m- TERCHANGE wrrn COMPRESSED GASES Application July 18, 1933, Serial No. 680,964 In Germany July 22, 1932 7 Claims. (01. 122-24.)

The present invention relates to a method and apparatus for the transfer of heat from compressed gases, particularly from gases generated by explosion in a closed chamber under constant 5 volume with development of high pressures, to other materials by conveying such gases to a heat exchanger, for example, a steam generator, a superheater, or other apparatus.

In recent times much work has been done upon 10 the withdrawal and the utilization oi the sensible heat of the exihaust gases of explosion chambers, especially of those employed in con-.

stant volume explosion turbine plants. The various proposals that have been made are based 15 upon the application of the fundamental principle that very high flow velocities can be attained with the high pressure gases and lead to suddenly increased coeflicients of heat transfer and thus of the quantities of heat transferred in 20 the heat exchanger. This result has been explained according to the most recently established theory as being due to the fact that the insulating or boundary layer of gases between the. inner core of the combustion gas stream and the heat transfer surfaces of the heat exchanger is destroyed by the high velocity gases. In view of this fact the effort has been made to increase arbitrarily the flow velocity of the gases as much as possible in order to insure the complete 3 destruction of this insulating layer.

Such a mode of operation would, however, have to be rejected as unsuitable with gases generated with solid fuels, such as coal dust. The erosion of the walls of the gas passageways by the sin- 35 tered, and therefore very hard ash particles of the powdered fuel increases to an extraordinary degree with the rebound velocity of the ash particles, as the. energy destroyed upon the impact is proportional approximately to the square of 40 the flow velocity. From this it will be clear that when very high gas velocities are resorted to to destroy the above-mentioned insulating layer, the erosion reaches values which cannot be tolerated because of the danger. it involves of impairing the strength of the heat exchanger.

Aside from this disadvantage in connection with the use of powdered fuels, the surprising fact has been established by me upon the basis of investigations with heat exchangers operating 50 with high velocities in the manner heretofore proposed, that the greatest heat transfer, contrary to established theory and to the accepted views of experts in this art, does not occur at all at the places of highest flow velocity. Proceeding 55 from'this discovery, the present invention involves the novel recognition that other influences than the high velocities are considerably more controlling and more determinative of the degree of heat transfer than the velocity. Upon closer investigation of these conditions in a boiler con- 5 sisting of a number of series of tubes which were fed with gases generated in an explosion chamber, it was established by exact measurements that the greatest heat transfer did not occur, as stated, at the places of highest velocity but in the gas collecting space which was connected to the last series of tubes of the boiler. This phenomenon that the greatest heat transfer took place in this collecting space was traced, upon closer study, to the fact that opportunity is afforded in the collecting space to the heating gases to whirl and eddy in all directions. In other words, the gas stream flowing at first through the individual slits between the series of tubes of the boiler in an essentially regular and uniformly directed current, acquires, after leaving the last slit between the series of tubes, that is, upon flowing into the open collecting space communicating with such slit, which in relation to the slit is of comparatively large volume, an irregular, disordered flow. 2'5 From this consideration it will be clear that the gas stream is broken up in the collecting space because of the whirling of its whole mass, so that now eventhe inner portions of the gas stream come into contact with the walls of the passage- 0 way (collecting space) and give up heat thereto. A certain degree of whirling naturally occurs also in known constructions in the narrow spaces between the individual series of tubes; such whirling is, however, of practically inconsequential effect, as it occurs to only a very slight degree at the surface of the gas stream and for that reason acts only as so-called marginal whirls. Because of the narrow intermediate spaces between the tubes no opportunity is consequently afforded the gas stream to come into'heat exchange throughout its whole mass with high whirling velocities as is the case in the comparatively large collecting space at the outlet end of the heat exchanger or boiler.

The present invention is thus based upon the discovery that for thoroughgoing utilization of the sensible heat contained in the compressed gases, for example, explosion gases, it is important deliberately to whirl the gas stream along its path through the heat exchanger. The advantages of such whirling, however, as I have further found, can be utilized only when the whole mass of gases to be charged into the heat exchanger is whirled and enough space is placed at the disposal of the gas whirls for their forma-' tion, while the actual heat exchange may begin only after the whirling of the gases and proceed under utilization of the whirling velocities. The latter can occur by bringing the whirls into heat exchanging contact with the walls defining the whirling spaces.

The correctness of the theory underlying the invention is confirmed upon closer consideration of the fact that up to the present time high velocities were considered essential for destroying the insulating layers in the gas stream, which, as already mentioned, form an obstacle to high heat interchange, and such high velocities had to be produced by corespondingly high pressure drops. As in such known procedure the gas stream acquires a very regular and uniform flow, extremely high velocities, and consequently high pressure drops are necessary to accomplish the destruction of the insulating film. The present invention, on the other hand, is based on the consideration that if there is utilized, not uniform and regular streams of gases, but rather irregular, disordered, and whirling streams, the same effect of a destruction of the insulating layer can be attained with a considerably smaller expenditure of energy. In addition, the insulating layer is more effectively destroyed than is the case when the gases fiow in a uniform stream. In this connection it may be mentioned that the earlier processes had the further important disadvantage that upon the production of the high velocities, not only the pressure, but also the temperature of the gases was considerably reduced in accordance with the adiabatic expansion process. The heat transfer in the heat exchanger is thus impaired also for the reason that the temperature difference between the heating gases and the heat transfer surfaces is reduced. Even if a definite, high heat transfer coefiicient for every sq. meter (degree C.) hour is attained the total quantity of heat exchanged will be smaller in view of the reduced temperature drop than would be the case if the original high temperature Was maintained.

The present invention embodies the discoveries above described and removes the above mentioned dimculties in the transfer of heat from compressed gases, and particularly from the gases discharged under pressure from explosion chambers, such as constant volume explosion chambers of the type employed in explosion turbine plants, to other materials, by deliberately causing violent whirling of the gases as their velocities are increased through reduction of their pressure along their path through the heat exchanger, and during such whirling bringing such gases into contact with the heat transfer surfaces. My improved mode of operation presents the following advantageous efiects:

In the first place, the greater part of the flow energy is destroyed by the whirling and is converted into temperature increases, so that the temperature prevailing before the expansion is again approximately reached. On the other hand, a completely irregular and non-uniform flow of the heating gases develops in the whirlproducing gas passageway. Such a flow breaks up the heating gases completely in consequence of the high whirling velocities of the whole mass of gas, so that all particles of gas are brought into heat exchange contact with the walls of the passageway, and thereby the formation of insulating layers, as in known processes, is effectively avoided. Furthermore, only a small amount of energy is necessary for producing the whirling velocities. With my improved efficient heat exchange process, any given capacity of heat interchange, particularly in steam boilers and superheaters, can be realized with a considerably smaller amount of heating surface as compared with heat interchangers operating according to known processes. Conversely, a heat exchanger of any given size can be considerably increased in capacity by my new process as compared with a heat exchanger of the same size operating according to known processes and principles. A further advantage of the invention resides in the fact that it is not necessary, as it has been up to the present time, to break up the gas stream mechanically into a very large number of tubes, which, as known, are very sensitive to erosion. For example, cast chambers can be employed with walls in which the dangers caused by erosion are reduced.

My new heat exchange process is particularly efficient when the heating gases are conducted through the suitably constructed gas passageway with stepwise reduction in pressure. This stepwise expansion of the gases brings with it the further advantage that by the fall of the pressure by smaller degrees than in the case of single stage expansion, in which according to experience very high velocities occur, the erosion in the case of operation with coal dust of the parts exposed to the gas stream is considerably smaller than in single stage expansion. In practical tests the stepwise expansion of the gases there did indeed appear non-uniform heat transmission in the gas passageway, but this could, however, be removed by suitable measures which are explained more in detail below.

In order to embody the process according to the invention in a practical construction, care must first of all be taken that the gas whirl can take place to a sufi'icient degree. To this end whirl producing media, such as deflecting or balile plates, may with advantage be arranged in the gas passageway; such baifle plates may themsleves form part of the heat transfer surfaces. A thorough whirling is obtained when provision is made for the breaking up of the gas stream in the whirl-producing chamber of the gas passageway by suitable inserts, and if desired, by deflecting the gas stream along its path.

Several embodiments of the invention are illustrated by way of example on the accompanying drawings in the form of a steam generator which is heated with the gases discharging under pressure from an explosion chamber which operates as a generator of hot combustion gases in a manner known in the art of constant volume explosion gas turbines.

In said drawings,

Fig. 1 shows diagrammatically a view, partly in section, of the whole steam plant together with the controlling mechanism for the explosion chamber;

Fig. 2 shows the steam generator in longitudinal section along the line II-II of Fig. 3, the heating surface of such generator being provided by a number of whirling chambers communicating with each other which are traversed in series by the heating gases;

Fig. 3 is a transverse vertical section along the lines III-III of Fig. 2;

Fig. 4 illustrates a horizontal section through v VI-VI of Fig. 2; V

the inlet end of the boiler according'to line IVIV of Fig. 3; a i Fig. 5 is a vertical section through the boiler along the line V-V of Fig. 2;

' Fig. 6 is a similar section according to line i Fig. 7 shows a longitudinal section of a second embodiment of the invention, the heating gases entering the same being fed through a-number of gas passages built in the form of tubes which are divided into spaced throttling places or chambers arranged in series;

Fig. 8 is a partial section of the boiler of Fig. 7 along the line VIII-VIII of such figure; and

Figs. 9 and 10 show two other arrangements for conducting the heating gases, the same being shown in partial longitudinal section.

Referring to Fig. 1, A indicates an elongated explosion chamber which serves as the gas generator of the plant, its function being similar to that in constant volume explosion turbine plants. The explosion chamber is equipped with various hydraulically operated members including the air valve B, the outlet or nozzle valve D andthe hydraulically controlled fuel pump P of known constructions, and is fed with fuel periodically by the injection member C. All of the hydraulically controlled members are operated, through conduits E1, E2 and E3 from a pressure medium distributor F of the type already proposed for explosion turbines. This distributor consists of arotating controlling cylinder G which is continuouslyand uniiormly rotated through gearing H by the motor J, and in accordance with the working cycle of the controlling members, alternately places the individual conduits E1, E2, E3, under pressure or relieves the conduits of pressure-for definite time intervals. The control medium may be pressure oil or any other suitable pressure medium, the same being conducted from the supplytank K with the aid of a pump L through conduit M and air chamber N to the hollow interior 0 of the rotating cylinder G, such interior being thus constantly under pressure.

The pump L which supplies thecontrol medium under pressure is likewise driven by the motor J. The operating media (air and fuel) introduced into the combustion chamber are ignited at the proper instant, after the formation of an ignitable mixture, by an igniting device, such as a spark plug Q. The high pressure, high temperature gases so generated in the chamber A are then discharged through the nozzle valve D into the nozzle channel R and thence pass into the steam boiler S, from which they discharge through the tube T aftergiving up all or any predetermined portion of their content of available heat. The boiler feed water is conducted to the boiler in preheated condition, such water being conducted through cooling jackets of the explosion chamber A and of the nozzle channel R, the water reaching the boiler S under high pressure through conduit U and the connected branch pipes in which the throttling member V1, V2, V3 are located. The feed water is strongly heated under pressure in the boiler by the gases delivered by the explosion chamber A, so that a considerable part thereof is converted into steam in the steam separator W after partial decompression of the heated water through the pressure reducing valve X. The steam so produced is withdrawn at Y, while the residual water is conducted by -pipe'W1 to the pump Z1. The water is fed at high pressure by the pump to the conduit W2 which leads it into the above mentioned cooling jackets of 'theexplosion duit Y in the form of steam. The pumps Z1 and Z2 are drivenby the electric motor J1.

The apparatus so far described is known and forms no part of the present invention. The invention is directed to the construction of the heat exchanger and to the economical utilization of the heat content of the high pressure gases generated in the explosion chamber. It will be understood that the explosion chamber illustrated is shown merely by way of example as one form of gas generator; any other type of gas generator and any'other suitable process for the production of high pressure gases having a heat content which can be economically utilized may be employed. Furthermore, the heating gases can be conducted into any suitable type of heat exchanger other than a boiler, while any desired number of gas generators may be employed.

The heat exchanger, shown in the form of a steam generator, is illustrated more in detail in Figs. 2 to 6. The numeral I indicates an outer boiler drum in which a smaller drum-like body 2 is positioned in such manner that between the drums I and 2 there is formed an annular space 3 which is concentric with the axis of the boiler. The feed water conduit 5 opens into this annular space, such conduit branching from the main feed waterconduit U (see Fig. 1). Upon the opposite side of the boiler drum I there is provlded a conduit 6 for leading ofi the water which has been heated'in the boiler. The body 2 consists of a number of lens-shaped chambers 1 arranged one after the other (twelve being shown in Fig. 2) which in the direction from one boiler end to the other are connected alternatinglyby a plurality of pipes 8 arranged near to the circumference of the space and by central passages ll, so that a very winding and tortuous path is provided for the gases inthe boiler. The individual connecting pipes '8, of which those in the same plane perpendicularly to the boiler axis and associated into a group have as nearly as possible the same total cross section as an adjoining central passage ll, each has a rib 9 directed toward the axis of the boiler which reinforces the connection between two opposite transverse walls ll] of two adjoining chambers I, such walls carrying the connecting pipes 8. r

The central passages H are formed by a deep contraction l2 in the outer wall of the insert body 2 which extends throughout the whole circumference of the latter. .In every contraction a plurality of radial ribs l3 are provided which connect the adjoining transverse walls [4 of the contractions. rigidly with each other, so that the annular space about each contraction is subdivided into sector-likeintermediate spaces 20 (see Fig. 5). As can best be seen from Figs. 5 and 6, the outer drum l is provided upon its inner wall in the horizontal plane with two opposite longitudinal flanges 2| which throughout their whole length lie against corresponding longitudinal flanges l5 upon the outer wall of the hollow body 2. In this way the annular space 3 between the outer drum l and the bodyl is divided into halves. The feed water flowing under pressure through conduit 5 into the annular space, 3 is thus forced to flow from below through-the sector-like spaces along the radial ribs 9', and I 3 into the upper half of the space 3; thefeedwater thus flows along a tortuous path throughitheannular space 3.

The first and last chambers 1 each communicate with a pipe l5 or I6 respectively. Both pipes are surrounded by a jacket I! or l8, respectively, serving as cooling chambers, the same being closed against the actual heating or boiling space (space 3) of the boiler. The cooling chambers are likewise fed with boiler feed water which is conducted thereto through branch conduits 5a, 5b, leading from the main feed water conduit U (Fig. 1), the water flowing off in heated condition through the conduits 6a and 6b.

The high pressure, high temperature gases generated in the explosion chamber A in Fig. 1 and flowing through the outlet valve D and the nozzle channel R pass through the pipe l5 under pressure and temperature into the steam generator and flow in succession through the series of chambers 7 by way of the pipes 8 and central passages l i. The high pressure gases are thus reduced in pressure to a definite extent in stepwise fashion from chamber to chamber, the interval between successive puffs being suitably adjacent to permit the pressure in the whirling chambers to fall to a sufficient degree, and finally in the last chamber, reach a definite counter pressure at which they leave the steam generator through exhaust pipe I6; the residual available energy still contained in the gases can then be utilized in any suitable heat engine or apparatus, as by producing the compression work for compressing the air required by the explosion chambers. In consequence of the high pressure difference, which exists as soon as the high pressure heating gases reach one of the chambers 1, there arises in each chamber 7 again and again a high gas flow velocity as successive discharges of gases enter the same. The heating gases upon their entry into the first chamber strike first against the transverse wall H) bounding such chamber, the gases then rebounding at right. angles in all directions and rushing with great turbulence toward the circumference of the chamber where they again flow off at right angles through the pipes 8 into the next chamber. Here the gases strike first the annular wall M of the first constriction I2 which faces them (see in the direction of gas fiow), where they are deflected at right angles back toward the center of the boiler where they flow off through the central passage ll into the next chamber. This mode of flow of the gases is repeated until the last chamber 1 is reached. Because of the fact that the high pressure heating gases again and again attain a high velocity at the throttling passage in advance of every succeeding chamber '1, in consequence of the considerable difference between the pressures in advance and to the rear of the successive throttling areas II, the gas stream upon entering any chamber 1 is directed with corresponding energy and violence against the impact or bafile surface l0 facing the throttling area or opening II. The gas stream is thus thrown into whirls, so that a disordered and irregular flow arises. The whole gas stream, including its core, is broken up, so that all of the gas particles whirl and eddy violently and come into contact with the walls of the chamber 1. The'whirling of the gas particles is still further considerably increased in accordance with the invention by the use of special whirl producing means, for example in the form of cam-like projections I9 in the gas passageway. Because of the fact that the flow velocity of the gases is converted into whirling velocity; the insulating layer which, as known, forms between the walls .of the gas passageway and the body of gases when the flow is uniform and regular, is destroyed and is broken up into its parts, or even prevented from forming so that all parts of the gases come frequently and repeatedly into contact with the surfaces of the gas passageway so that an extraordinarily high rate of heat transmission is obtained.

This procedure is repeated in every chamber 1, which in view of its action may best be designated as a whirling chamber. The surfaces exposed directly to the gas whirls in the gas passageway deliver the absorbed heat to the feed water which, as already indicated above, through the tortuous flow in the annular space 3 likewise contacts the heat exchange surface frequently and upon all sides, so that finally the water flows off in highly heated condition through conduit 6 to the steam separator W as shown in Fig. 1.

By the conversion of the flow velocity of the heating gases into whirling velocity in accordance with the invention there are obtained in particular three advantageous efiects. In the first place, the change in the condition of flow of the heating gases in the steam generator from uniform flow toturbulent whirling prevents the formation or the continuance of the insulating layer between the metallic walls of the gas passageway and the mass of gases, which ordinarily strongly hinders the heat transfer. Secondly, only comparatively small amounts of energy are required in my improved process for destroying such insulating layer of gas, because the completely irregular and disordered flow which is represented by whirling flow destroys the insulating layer much easier than does a. continually uniformly directed and regular flow, such as is obtained in normal adiabatic expansion. Finally, as already indicated above, all portions of the mass of hot gases are brought into contact with the heat transferring walls defining the gas path, so that by the combination of these three effects extraordinarily high degrees of heat interchange are secured.

As the heat interchange in the first part of the boiler (first whirling chamber), because of the fact that the heating gases at such point have their highest temperature and pressure, is very high, as will readily be understood (and has been confirmed by tests on a practical scale), these magnitudes falling in value in the next following whirling chambers toward the opposite end of the boiler, I provide measures for further improving the new working process according to the invention by reducing the temperature stresses at the inlet end of the boiler in order to subject the heating surfaces to stresses substantially uniformly throughout the gas passageways and thereby equalize as far as possible the heat interchange along the whole length of the boiler. To solve this problem in the simplest and most efficient manner possible, I have given consideration to the fact that the coefiioient of heat transfer depends mainly upon the following three factors of the heating gases: pressure, temperature and velocity. From the fact that the pressure and temperature are magnitudes which cannot readily be influenced, I have recognized that, of the three above mentioned factors, for influencing the heat transfer in the gas passageway, only the velocity can from a practical standpoint be considered. According to the invention, this factor is controlled in such a manner that it increases toward the outlet end of the boiler. This increase in velocity is obtained by suitable selection of the size of'the cross sections of the passages 8, l I between the expansion stages in the gas conduit. As experiments' have shown, very favorable 1 conditions arise when the cross section of flow is reduced from stage to stage in the direction of gas flow, and is then again increased in the last stage or stages of the heat exchanger; the latter taking into consideration the change in volume of the gases. The desired effect can, however, at least approximately, be attained if the cross sectional areas of flow increase or are made approximately equal in size, an increase in velocity resulting from the increase in volume of the gases. In the construction of Fig. 2 the flow areas diminish in size toward the outlet end of the boiler up to the last central passageway II and the inlet pipes 8 of the last whirling chamber 1. This last central passageway and these last connecting pipes, however, increase in cross section as compared with the preceding passageway l I and pipes 8. In this way the result is obtained that the velocity of the heating gases increases toward the outlet end of the boiler, while the pressure and temperature of the gases naturally fall in the same direction. As a result of the opposite changes in the controlling magnitudes for the coefiicient of heat transfer,

it is possible to maintain the heat transfer at all parts of the gas path at a value at which dangerous stresses in the boiler are avoided.

In the construction of the whirling flow boiler for carrying out the process of the invention care must be taken not to make the whirling chambers too large. In the development of the constant volume explosion gas turbine the space immediately behind the outlet member of the explosion chamber has played a very important role. This space,

which in the constant volume explosion chambers developed by me'has been termed the nozzle channel, must first be filled with explosion gases as soon as the outlet member of the explosion chamber is opened. Such initial filling is accompanied by a definite loss in pressure and in output, which becomes particularly large when gases simultaneously escape from the space to be filled. during such filling process. In order, therefore, to keep small this unavoidable loss of pressure and output which is associated with the filling of the whirling chambers, it will be ofadvantage not to make the whirling chamber 1 of the heat exchanger larger than is necessary just to effect sufficient whirling. In other words, the whirling chambers are made as narrow as possible (see Fig. 2) In this way the loss accompanying the filling of such chambers with gases is reduced to a minimum.

Figs. 7 and 8 illustrate another form of construction of the boiler, the same having a plurality of gas and water conduits arranged for the :most part parallel to each other. The boiler consists of an outer cylindrical 'shell 22 upon whose ends an arched dome-like head 23 is attached in drical portion 24 of the boiler head 23 and'is attached thereto by welding or otherwise. Between the cupola shaped boiler head 23 and the end member 26 of both ends of the boiler, there is a cone-shaped space 21. The end member 26 in the upper boiler part 'is'penetrated by a plurality of short watertubes 28 which connectthe upper space 21 with the central zone of the boiler. The two rings 25 carry a number of tubes 29 lying upon the arc of a circle and running parallel with the boiler axis, such tubes connecting the two cone-shaped spaces 2'! with each other. These tubes are connected in water and gas-tight man ner with the holding rings 25 and are penetrated by tubes 30 of smaller diameter arranged concentrically within the tubes 29. The ends of the interior tubes 30, which are traversed by the water or other heat-receiving medium, are fixed in gas and water-tight manner within suitable openings in the outermost walls of the end memture stress'in the gas contacted walls of the gas passageways and of the volume change of the gases in the direction of gas flow, the bores or passages 32 in the throttling rings vary in diameter, as is indicated at'the left side of the boiler in Fig. 7 by the inclined dash line 31.

The spaces between the inner tubes 30 and the outer edges of the passageways 32 serve as throttling places for the heating gases which flow through the pipe 33 in highly compressed condition, and after leaving the expansion stage or chamber 30d of the outer tube 29 flow off through c the upper end member 26 and its connecting pipe 34. The gas tubes 29 are swept upon their outer surface by the heat-receiving substance (water) which is introduced at 35 in the lower boiler head 23 and flows off in highly heated condition or in the form of steam at 36 in the upper boiler head.

The operation of the boiler just described is as follows: I

The gases entering the boiler at 33 at high pressure and temperature flow through the lower end member 26 and then through the first throttling place defined by the intermediate space between the edges of the passageway 32 and the outer surface of the water-filled inner tube 30. In consequence of the considerable difference between the pressure on the two sides of such throttling place, high velocities are developed at such places. Because of the sudden enlargement in the cross-section of flow behind the throttling place 32 in the space 30a, the flow energy is en tirely, or at least for the greater part, converted into whirling velocities. As a result, further, of this whirling, similarly to the first described embodiment of the boiler, a correspondingly high heat transfer to the gas contacted wall surfaces of the space 30a occurs, such heat being transmitted to the water which sweeps the outer surface of the tubes 29 and the inner surface of the tubes 30 within the range of the space 30a. I-Iereupon the gasesfiow through the second throttling place 'into the next chamber 30b and with approximately the same velocity as before, such velocity "developing because of the high pressure difference which again prevails between the spaces in advance of and to the rear of such second throttling place. The gases are again thrown into whirl with the result that a high rate of heat interchange again occurs. This process is repeated as often as a throttling place and heat transfer surfaces are encountered by the gases. As the.

pressure and temperature fall from expansion stage to expansion stage, the throttling areas vary in accordance with the line 37 in order'to increase the flow velocity of the gases toward the end of the boiler. In this way the rate of heat transmission is maintained approximately uniform for the whole length of the gas passageway in the boiler so that unpermissibly high stresses in the Walls of the boiler in consequence of high temperature differences along the gas passageways are avoided. I

As shown in Fig. 9 the whirling of the gases in the individual expansion chambers of the gas passageway can be increased considerably with the aid of inserts of suitable nature, for example, by means of'rings 38 which are supported upon the inner tube 30 and operate to deflect the gas stream. The throttling rings 3| or the rings 38 can, of course, be formed by indentations in the walls of the tubes 29 and 3!]. Such an arrangement is shown in Fig. 10 in which the gas and water tubes are expanded inwardly or outwardly at the throttling places to form an annular projection which constricts the gas passageway.

It will be noted that in each of the embodiments of the invention above described the gases as they emerge at increased velocity from the constricted area or throttling point strike hollow walls that are swept by the medium to be heated and thus are protected against destruction by the hot gases. These hollow walls may be formed in various ways, as by being made re-entrant, as exemplified by the walls I0 and M of Fig. 2, or tubular, as shown at 3|] in Figs. 9 and 10.

What has been said hereinabove for steam boilers applies naturally also for other types of heat exchangers, as for pre-heaters and superheaters. It is likewise also possible to vary considerably the construction of the boiler and the form of the gas passageways without departing from the principles of the invention.

I claim:

1. The method of'transferring heat from intermittent puffs of hot gases of high pressure, such as the live gases discharging from a constant volume explosion chamber, to a substance of lower temperature, which comprises reducing the pressure of the successive puff of gases in stepwise fashion as they pass in heat transmitting relation with such substance and thereby repeatedly imparting to such gases a high velocity and directingthe high velocity gases repeatedly into a relatively large space wherein their velocity in the general direction of flow is reduced and their kinetic energy in part converted into whirls and eddies whereby the whole mass of gas is set into turbulent agitation and all parts thereof caused to come into contact with the heat transfer surfaces between the gases and said substance, the puifs being only of such frequency that the pressure in eachspace' falls to a pressure substantially below that of the incoming puff of pressure gases before the latter arrives.

2. The method according to claim 34, wherein the gases as they expand and attain increased velocities are directed against heat transfer surfaces cooled by the medium to be heated and lying transversely to'the path of the gases, the gases rebounding violently from such surfaces and their velocity being converted in large part into whirls and eddies.

3. In a'heat exchanger, the combination'of a conduit for conducting hot gases under pressure to said exchanger, a plurality of gas whirling chambers arranged in series within the exchanger and receiving the gases from said conduit, and throttling channels of smaller cross-section than said chambers for connecting the chambers in series, whereby said gases expand in stepwise fashion through the successive throttling channels and into the next adjoining chamber, the cross-section of the throttling channels decreasing in the direction from the inlet toward the outlet end of the heat exchanger, and means for conducting a medium to be heated into contact with'the gas-impinged walls of the heat exchanger.

4. In a heat exchanger, the combination of a conduit for conducting hot gases under pressure to said exchanger, a plurality of gas whirling chambers arranged in series within the exchanger and receiving the gases from said conduit, and throttling channels of smaller cross-section than said chambers for connecting the chambers in series, whereby said gases expand in stepwise fashion through the successive throttling channels and into the next adjoining chamber, the cross-section of the throttling channels decreasing in the direction from the inlet toward the outlet "end of the exchanger, up to, but not including the last channel, such last channel being of greater cross-sectional area than the channel preceding the same, and means for conducting a medium to be heated into contact with the gas impinged walls of the heat exchanger.

5. The method of transferring heat from hot gases of high pressure, such as the gases'discharging from explosion chambers, to a substance of lower temperature, which comprises reducing the pressure of the gases in stepwise fashion as they pass in heat transmitting relation with such substance and thereby repeatedly imparting to such gases a high velocity, causing the gas stream. to whirl throughout its whole mass during each partial expansion and bringing the whirling gases into contact with the heat transfer surfaces between the gases and said substance, and increasing the flow velocity of the gases toward the discharge end of the heat exchanging path in such a manner that the rates of heat transfer in the individual expansion stages along the path of the gases assume values within the limits of permissible stresses in the said heat transfer surfaces.

6. A heat exchanger having conduits for conducting thereinto intermittent puffs of high pressure explosion gases and a medium to be heated for heat exchange therein, and a gas passageway within the exchanger having re-entrant walls extending inwardly of the passageway and forming successive constrictions between spaces of relatively large volume, said constrictions being formed by annular inwardly expanded portions of the passageway, the gases being thus throttled at said constrictions and their pressure reduced with accompanying increase in their velocity, a re-entrant wall being positioned opposite the outlet of the constriction formed by the preceding re-entrant wall so as to be impinged by the gases emerging therefrom, the medium to be heated having access to said re-entrant walls to cool the same.

7. In a heat exchanger, a conduit for conducting intermittent puffs of hot high pressure gases to said heat exchanger, a pipe for conducting a medium to be heated to the heat exchanger, and means in said heat exchanger providing a passageway for said gases there'- through which presents successive constrictions 'of the gas stream before they continue their at which the flow of the gases is throttled and the pressure of the gases reduced in step-wise fashion and their velocity repeatedly increased, said means including hollow walls contacted by the medium to be heated and arranged in relation to the successive constrictions to provide obstructing surfaces in the path of the gases against which the gases strike violently as they emerge at increased velocity from the associated constrictions and from which they rebound with conversion of their rectilinear velocity into irregular whirls and eddies reaching to the core flow-through the heat exchanger, the passageway for the gases being comprised of a tube having spaced inwardly extending annular projections dividing such tube into a plurality of successive chambers and providing the aforementioned constrictions, said projections being formed by inwardly expanded portions of said tube, all of the walls contacted by the gases being in cooling contact with the medium to be heated.

' HANS HOLZWARTH. 

